The project involves development and testing of new biodegradable drug delivery systems. The systems being synthesized are polymers of L-glutamic acid to which a grogestin, namely, norethindrone, is covalently bonded. The polymers are then tested by in vitro and in vivo methods using labeled norethindrone to determine the release characteristics of the steroid from the polymeric backbone. The workscope also includes inspection of implant sites in animals for gross pathology and histopathology. Polymer-drug combinations and breakdown products are also tested in guinea pigs and rabbits for potential immunogenicity.